European patent application n° 1 187 423 describes a method of transmitting on-demand information whose content varies with time, like music or video. In particular, it describes a so-called buffering distribution method that consists in dividing a single piece of content into a plurality of files (also called slices) and in downloading the content file by file, starting from the first file. This buffering distribution method is described as providing the advantage of reducing the waiting time before starting playback (while part N is being downloaded, part N−1 can be played).
However, when a slice is transmitted in the form of packets using a non-reliable protocol, some errors might occur during the transmission of packets.
A first solution to this problem is the conventional data carrousel, used for example in satellite broadcasting network. Thanks to this data carrousel, a file is played cyclically and is accessed packet by packet. But, when a packet of a file is corrupted or lost, the receiver must wait until the carousel cycles again to get the missing packet so that the time to wait is the duration of the file.
A second solution is retransmission. In this case, when a packet is lost, the receiver must ask for it to be transmitted again, which is not possible if there is no return channel (e.g. pure broadcast) and does not scale well otherwise because the sender can get very busy sending retransmitted packets for each receiver. The bandwidth usage can be also dramatically increased when many retransmissions are required.